Process for etching a metal layer suitable for use in photomask fabrication

ABSTRACT

Method and apparatus for etching a metal layer disposed on a substrate, such as a photolithographic reticle, are provided. In one aspect, a method is provided for processing a substrate including positioning a substrate having a metal layer disposed on an optically transparent material in a processing chamber, introducing a processing gas processing gas comprising an oxygen containing gas, a chlorine containing gas, and a chlorine-free halogen containing gas, and optionally, an inert gas, into the processing chamber, generating a plasma of the processing gas in the processing chamber, and etching exposed portions of the metal layer disposed on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/616,990, filed Dec. 28, 2006, now U.S. Pat. No. 7,682,518, whichapplication is a continuation of U.S. patent application Ser. No.10/925,887, filed Aug. 25, 2004, now U.S. Pat. No. 7,521,000, whichapplication claims benefit of U.S. Provisional Patent Application Ser.No. 60/498,730, filed Aug. 28, 2003, all applications of which areincorporated by reference in their entireties. Priority to the filingdates of these applications is claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the fabrication of integrated circuitsand to the fabrication of photolithographic reticles useful in themanufacture of integrated circuits.

2. Background of the Related Art

Semiconductor device geometries have dramatically decreased in sizesince such devices were first introduced several decades ago. Sincethen, integrated circuits have generally followed the two year/half-sizerule (often called Moore's Law), which means that the number of deviceson a chip doubles every two years. Today's fabrication plants areroutinely producing devices having 0.15 μm and even 0.13 μm featuresizes, and tomorrow's plants soon will be producing devices having evensmaller geometries.

The increasing circuit densities have placed additional demands onprocesses used to fabricate semiconductor devices. For example, ascircuit densities increase, the widths of vias, contacts and otherfeatures, as well as the dielectric materials between them, decrease tosub-micron dimensions, whereas the thickness of the dielectric layersremains substantially constant, with the result that the aspect ratiosfor the features, i.e., their height divided by width, increases.Reliable formation of high aspect ratio features is important to thesuccess of sub-micron technology and to the continued effort to increasecircuit density and quality of individual substrates.

High aspect ratio features are conventionally formed by patterning asurface of a substrate to define the dimensions of the features and thenetching the substrate to remove material and define the features. Toform high aspect ratio features with a desired ratio of height to width,the dimensions of the features are required to be formed within certainparameters that are typically defined as the critical dimensions of thefeatures. Consequently, reliable formation of high aspect ratio featureswith desired critical dimensions requires precise patterning andsubsequent etching of the substrate.

Photolithography is a technique used to form precise patterns on thesubstrate surface, and then the patterned substrate surface is etched toform the desired device or features. Photolithography techniques uselight patterns and resist materials deposited on a substrate surface todevelop precise patterns on the substrate surface prior to the etchingprocess. In conventional photolithographic processes, a resist isapplied on the layer to be etched, and the features to be etched in thelayer, such as contacts, vias, or interconnects, are defined by exposingthe resist to a pattern of light through a photolithographic reticlehaving a photomask layer disposed thereon. The photomask layercorresponds to the desired configuration of features. A light sourceemitting ultraviolet (UV) light or low X-ray light, for example, may beused to expose the resist in order to alter the composition of theresist. Generally, the exposed resist material is removed by a chemicalprocess to expose the underlying substrate material. The exposedunderlying substrate material is then etched to form the features in thesubstrate surface while the retained resist material remains as aprotective coating for the unexposed underlying substrate material.

Binary photolithographic reticles typically include a substrate made ofan optically transparent silicon-based material, such as quartz (i.e.,silicon dioxide, SiO₂), having an opaque light-shielding layer of metal,or photomask, typically chromium, disposed on the surface of thesubstrate. The light-shielding layer is patterned to correspond to thefeatures to be transferred to the substrate. Binary photolithographicreticles are fabricated by first depositing a thin metal layer on asubstrate comprising an optically transparent silicon-based material,and then depositing a resist layer on the thin metal layer. The resistis then patterned using conventional laser or electron beam patterningequipment to define the critical dimensions to be transferred to themetal layer. The metal layer is then etched to remove the metal materialnot protected by the patterned resist; thereby exposing the underlyingoptically transparent material and forming a patterned photomask layer.Photomask layers allow light to pass therethrough in a precise patternonto the substrate surface.

Conventional etching processes, such as wet etching, tend to etchisotropically, which can result in an undercut phenomenon in the metallayer below the patterned resist. The undercut phenomenon can producepatterned features on the photomask that are not uniformly spaced and donot have desired straight, vertical sidewalls, thereby losing thecritical dimensions of the features. Additionally, the isotropic etchingof the features may overetch the sidewalls of features in high aspectratios, resulting in the loss of the critical dimensions of thefeatures. Features formed without the desired critical dimensions in themetal layer can detrimentally affect light passing therethrough andresult in less than desirable patterning by the photomask in subsequentphotolithographic processes.

Plasma etch processing, known as dry etch processing or dry etching,provides a more anisotropic etch than wet etching processes. The dryetching process has been shown to produce less undercutting and toimprove the retention of the critical dimensions of the photomaskfeatures with straighter sidewalls and flatter bottoms. However, dryetching may overetch or imprecisely etch the sidewalls of the openingsor pattern formed in the resist material used to define the criticaldimensions of the metal layer. Excess side removal of the resistmaterial results in a loss of the critical dimensions of the patternedresist features, which may translate to a loss of critical dimensions ofthe features formed in the metal layer defined by the patterned resistlayer. Further, imprecise etching may not sufficiently etch the featuresto provide the necessary critical dimensions. Failure to sufficientlyetch the features to the critical dimensions is referred to as a “gain”of critical dimensions. The degree of loss or gain of the criticaldimensions in the metal layer is referred to as “etching bias” or “CDbias”. The etching bias can be as large as 120 nm in photomask patternsused to form 0.14 μm features on substrate surfaces.

The loss or gain of critical dimensions of the pattern formed in themetal layer can detrimentally affect the light passing therethrough andproduce numerous patterning defects and subsequent etching defects inthe substrate patterned by the photolithographic reticle. The loss orgain of critical dimensions of the photomask can result in insufficientphotolithographic performance for etching high aspect ratios ofsub-micron features and, if the loss or gain of critical dimensions issevere enough, the failure of the photolithographic reticle orsubsequently etched device.

Therefore, there remains a need for a process and chemistry for etchinga metal layer on a substrate, such as a reticle, to produce a patternwith desired critical dimensions in the metal layer.

SUMMARY OF THE INVENTION

Aspects of the invention generally provide methods and related chemistryfor etching a photomask layer for a photolithographic reticle. In oneaspect, a method is provided for processing a photolithographic reticleincluding positioning the reticle on a support member in a processingchamber, wherein the reticle comprises a metal photomask layer formed onan optically transparent substrate and a patterned resist materialdeposited on the metal photomask layer, introducing a processing gascomprising an oxygen containing gas, a chlorine containing gas, and achlorine-free halogen containing gas, delivering power to the processingchamber to generate a plasma of the processing gas, and removing exposedportions of the metal photomask layer.

In another aspect, a method is provided for processing aphotolithographic reticle including positioning the reticle on a supportmember in a processing chamber, wherein the reticle comprises achromium-based photomask layer formed on an optically transparentsilicon-based material and a patterned resist material deposited on thechromium-based photomask layer, introducing a processing gas comprisingchlorine gas, oxygen gas, and hydrogen bromide, maintaining a chamberpressure between about 2 milliTorr and about 20 milliTorr, delivering asource power between about 100 and about 1000 watts to a coil disposedin the processing chamber to generate a plasma, supplying a bias powerto the support member between about 0 and about 150 watts, and etchingexposed portions of the chromium-based photomask layer, and removing thechromium-based photomask layer at a removal rate ratio of chromium-basedphotomask layer to resist material of about 1:1 or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited aspects of the inventionare attained and can be understood in detail, a more particulardescription of the invention, briefly summarized above, may be had byreference to the embodiments thereof which are illustrated in theappended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic cross-sectional view of one embodiment of anetching chamber;

FIG. 2 is a flow chart illustrating one embodiment of a sequence forprocessing a substrate according to one embodiment of the invention;

FIGS. 3A-3D are cross-sectional views showing an etching sequence ofanother embodiment of the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

Aspects of the invention will be described below in reference to aninductively coupled plasma etch chamber. Suitable inductively coupledplasma etch chambers include the ETEC Tetra I™ photomask etch chamberand the ETEC Tetra II™ photomask etch chamber, available from ETEC ofHayward, Calif., or optionally, a Decoupled Plasma Source (DPS I™, DPSII™, and DPS +™) processing chamber available from Applied Materials,Inc., of Santa Clara, Calif.

Other process chambers may be used to perform the processes of theinvention, including, for example, capacitively coupled parallel platechambers and magnetically enhanced ion etch chambers as well asinductively coupled plasma etch chambers of different designs. Examplesof such suitable processing chambers are disclosed in U.S. patentapplication Ser. No. 09/325,026, filed on Jun. 3, 1999, which isincorporated by reference to the extent not inconsistent with the claimsand disclosures described herein. Although the processes areadvantageously performed with the ETEC Tetra™ photomask etch chamber,the description in conjunction with the DPS™ processing chamber isillustrative, and should not be construed or interpreted to limit thescope of any aspect of the invention.

FIG. 1 is a schematic cross-sectional view of one embodiment of a DPS™processing chamber that may be used for performing the processesdescribed herein. The processing chamber 10 generally includes acylindrical sidewall or chamber body 12, an energy transparent dome 13mounted on the body 12, and a chamber bottom 17. A flat lid (not shown)or other alternative lid capable of being used with an inductive coilmay be used in place of the dome 13. An inductive coil 26 is disposedaround at least a portion of the dome 13. The chamber body 12 and thechamber bottom 17 of the processing chamber 10 can be made of a metal,such as anodized aluminum, and the dome 13 can be made of an energytransparent material such as a ceramic or other dielectric material.

A substrate support member 16 is disposed in the processing chamber 10to support a substrate 20 during processing. The support member 16 maybe a conventional mechanical or electrostatic chuck with at least aportion of the support member 16 being electrically conductive andcapable of serving as a process bias cathode. While not shown, a reticleadapter may be used to secure the reticle on the support member 16. Thereticle adapter generally includes a lower portion milled to cover anupper portion of the support member and a top portion having an openingthat is sized and shaped to hold a reticle. A suitable reticle adapteris disclosed in U.S. Pat. No. 6,251,217, issued on Jun. 26, 2001, whichis incorporated herein by reference to the extent not inconsistent withaspects and claims of the invention.

Processing gases are introduced into the processing chamber 10 from aprocess gas source 21 through a gas distributor 22 peripherally disposedabout the support member 16. Mass flow controllers (not shown) for eachprocessing gas, or alternatively, for mixtures of the processing gas,are disposed between the processing chamber 10 and the process gassource to regulate the respective flow rates of the process gases. Themass flow controllers can regulate up to about 1000 sccm flow rate foreach processing gas or processing gas mixture.

A plasma zone 14 is defined by the process chamber 10, the substratesupport member 16 and the dome 13. A plasma is formed in the plasma zone14 from the processing gases using a coil power supply 27 to power theinductor coil 26 to generate an electromagnetic field in the plasma zone14. The support member 16 includes an electrode disposed therein, whichis powered by an electrode power supply 28 and generates a capacitiveelectric field in the processing chamber 10. Typically, RF power isapplied to the electrode in the support member 16 while the body 12 iselectrically grounded. The capacitive electric field is transverse tothe plane of the support member 16, and influences the directionality ofcharged species to provide more vertically oriented anisotropic etchingof the substrate 20.

Process gases and etchant byproducts are exhausted from the processchamber 10 through an exhaust system 30. The exhaust system 30 may bedisposed in the bottom 17 of the processing chamber 10 or may bedisposed in the body 12 of the processing chamber 10 for removal ofprocessing gases. A throttle valve 32 is provided in an exhaust port 34for controlling the pressure in the processing chamber 10. An opticalendpoint measurement device can be connected to the processing chamber10 to determine the endpoint of a process performed in the chamber.

While the following process description illustrates one embodiment ofetching a substrate using processing gases as described herein, theinvention contemplates the use of processing parameters outside theranges described herein for performing this process in differentapparatus, such as a different etching chamber, and for differentsubstrate sizes, such as photolithographic reticles for 300 mm substrateprocessing.

Exemplary Etch Process

While the following description illustrates one embodiment of a processsequence for etching metal layers, such as chromium and chromiumoxynitride, as photomasks in photolithographic reticle fabrication, itis contemplated that the etching gases may be used to etch othermaterial layers formed on substrates in semiconductor andphotolithographic reticle manufacturing.

Generally a photolithographic reticle includes an opaque layer, known asa photomask, deposited on an optically transparent substrate. The opaquelayer may comprise a metal layer, for example, chromium, or anothermaterial known or unknown in the art suitable for use as a photomask.For example, the invention contemplates that the opaque layer maycomprise a non-metallic dielectric material. An optically transparentmaterial of the substrate is broadly defined to include, but not limitedto, a material transparent to light having wavelengths of about 300 nmor less, for example, transparent to ultraviolet light havingwavelengths of 248 nm and 193 nm.

FIG. 2 is a flow chart of one embodiment of one process sequence of anetching process 200. The flow chart is provided for illustrativepurposes and should not be construed as limiting the scope of anyaspects of the invention. FIGS. 3A-3C illustrate the composition of thephotolithographic reticle at points during the photomask forming processas well as further illustrate the process described above in FIG. 2.

A substrate 300, typically comprising an optically transparent material310, such as optical quality quartz, fused silica material, molybdenumsilicide (MoSi), molybdenum silicon oxynitride (MoSi_(X)N_(Y)O_(Z)),calcium fluoride, alumina, sapphire, or combinations thereof, isprovided to a processing chamber at step 210, such as the DPS™processing chamber 10 of FIG. 1.

The substrate is then processed by depositing an opaque metal layer 320as a metal photomask layer, typically comprising chromium, on thesubstrate material 310 at step 220 as shown in FIG. 3A. The chromiumlayer may be deposited by conventional methods known in the art, such asby physical vapor deposition (PVD) or chemical vapor deposition (CVD)techniques. The metal layer 320 is typically deposited to a thicknessbetween about 50 and about 100 nanometers (nm); however, the thicknessof the metal layer 320 may differ based upon the requirements of themanufacturer and the composition of the materials of the substrate ormetal layer.

Optionally, an anti-reflective coating (ARC or ARC layer) may be formedon or comprise part of the deposited metal layer 320. The ARC layer isbelieved to improve photolithographic precision in patterning featuresto be formed in the opaque layer. The ARC layer may be a metal layerincorporating nonmetallic contaminants or impurities to form, forexample a metal oxynitride layer, such as chromium oxynitride. Chromiumoxynitride may be formed during deposition of the metal layer or byexposing the metal layer to a suitable atmosphere, such as an oxidizingand nitrating environment. Alternatively, the chromium oxynitride layermay be deposited by conventional methods known in the art, such as byphysical vapor deposition (PVD) or chemical vapor deposition (CVD)techniques. The metal oxynitride layer may comprise up to the top 25% ofthe total thickness of the metal layer 320.

The optional ARC layer is typically formed at a thickness between about10 nanometers (nm) and about 15 nm; however, the thickness of the layermay differ based upon the requirements of the manufacturer and thecomposition of the materials of the substrate or metal layer, and may bemainly concentrated in the upper surface of the deposited material, suchas the upper 30% of the thickness of the original metal layer 320. Thechromium oxynitride film is believed to be more sensitive to etchingwith oxygen radicals than chromium films. A reduced amount of oxygen inthe processing gas may be used to effectively etch the chromiumoxynitride surface compared to etching the bulk of the remainingchromium material.

The dimensions of openings or patterns in the metal layer 320 arepatterned by depositing and pattern etching a resist material 330 toexpose the metal layer 320 at step 230 as shown in FIG. 3B. The resistmaterials used in photolithographic reticle fabrication are usually lowtemperature resist materials, which are defined herein as materials thatthermally degrade at temperatures above about 250° C., an example ofwhich includes “ZEP,” manufactured by Hoya Corporation or othersdescribed herein. The resist material 330 is deposited upon the metallayer 320 to a thickness between about 200 nm and about 600 nm.

The resist material may be a photoresist material, which may bepatterned optically using a laser patterning device or by anotherradiative energy patterning device, such as an electron beam emitter toform a pattern 325 that is used to define the dimensions of the featuredefinition to be formed in the metal layer 320.

The opaque, metal layer then is etched to produce a photomask layerhaving features with desired critical dimensions. The substrate 300 isthen transferred to an etch chamber, such as the DPS™ processing chamber10 described above, for etching the metal layer 320. Openings andpatterns 335 are formed in the metal layer 320 by etching the metallayer using the processing gas described herein including the oxygencontaining gas, chlorine containing gas, chlorine-free halogencontaining gas, and optionally, an inert gas, to expose the underlyingoptically transparent substrate material, and optionally, an ARC layer,at step 240 as shown in FIG. 3C.

Etching of exposed portions of the opaque metal layer 320 occurs bygenerating a plasma of a processing gas by supplying a source powerand/or a bias power to the processing chamber. The processing gasincludes an oxygen containing gas, a chlorine-containing gas, achlorine-free halogen containing gas, and optionally, an inert gas, foretching the metal layer.

The oxygen containing gas is selected from the group comprising one ormore of oxygen (O₂), carbon monoxide (CO), carbon dioxide (CO₂), andcombinations thereof, of which oxygen is preferred. The oxygencontaining gas provides a source of etching radicals and carbon monoxide(CO) and carbon dioxide (CO₂) gases may provide a source of material forforming passivating polymer deposits, which may improve etch bias.

The chlorine containing gas is selected from the group comprising one ormore of chlorine gas (Cl₂), carbon tetrachloride (CCl₄), hydrogenchloride (HCl), and combinations thereof, of which Cl₂ is preferred,which are used to supply highly reactive radicals to etch the metallayer. The chlorine containing gas provides a source of etching radicalsand components, such as carbon tetrachloride (CCl₄) gas, that mayprovide a source of material for forming passivating polymer depositsthat may improve etch bias.

The chlorine-free halogen containing gas is selected from the groupcomprising one or more of hydrogen bromide (HBr), hydrogen iodide (HI),and combinations thereof, of which HBr is preferred. Hydrogen bromidemay also be delivered to processing from an aqueous solution or have anaqueous component as hydrobromic acid. The chlorine-free halogencontaining gas is used to supply both reactive radicals to etch themetal layer as well as hydrogen, which may reduce photoresist and metaletch rates and passivate the photoresist and metal sidewalls to minimizeoveretching and preserve desired critical dimensions, and improve etchbias.

The chlorine containing gas and the chlorine-free halogen containing gasare provided in a molar ratio of chlorine containing gas to thechlorine-free halogen containing gas between about 10:1 and about 0.5:1,for example, a chlorine to hydrogen bromide molar ratio between about10:1 and about 0.5:1.

The processing gas may also include an inert gas which, when ionized aspart of the plasma including the processing gas, results in sputteringspecies to increase the etching rate of the features. The presence of aninert gas as part of the plasma may also enhance dissociation of theactive processing gases. Examples of inert gases include argon (Ar),helium (He), neon (Ne), xenon (Xe), krypton (Kr), and combinationsthereof, of which argon and helium are generally used. The inert gasestypically comprise between about 5 vol % and about 40 vol %, such asbetween about 15 vol % and about 25 vol % of the total gas flow for theprocess. For plasma striking to initiate the plasma prior to introducingthe etching processing gas, the inert gas may comprise between about 75vol % and about 100 vol % of the process gas used.

The total flow rate of the processing gas, including the inert gas, isintroduced at a flow rate between about 100 sccm and about 700 sccm foretching a 150 mm by 150 mm square photolithographic reticles in an etchchamber. The oxygen containing gas may be introduced into the processingchamber at a flow rate between about 5 sccm and about 200 sccm, forexample, about 12 sccm, the chlorine containing gas is introduced intothe processing chamber at a flow rate of between about 5 sccm and about250 sccm, for example, about 96 sccm, and the chlorine-free halogencontaining gas is introduced into the processing chamber at a flow rateof between about 5 sccm and about 250 sccm, for example, between about10 sccm and about 50 sccm. When the inert gas is introduced into theprocessing chamber, a flow rate between about 25 sccm and about 100 sccmmay be used for etching a 150 mm by 150 mm square photolithographicreticles in the etch chamber.

The individual and total gas flows of the processing gases may varybased upon a number of processing factors, such as the size of theprocessing chamber, the size of the substrate being processed, and thespecific etching profile desired by the operator.

Generally, a source RF power level of about 1000 watts or less isapplied to an inductor coil to generate and sustain a plasma of theprocessing gases during the etching process. A power level between about100 watts and about 1000 watts, such between about 250 watts and about650 watts, has been observed to provide sufficient plasma of theprocessing gases for etching the substrate surface. The recited sourceRF power levels have been observed to produce sufficient etchingradicals and polymerization radicals from the processing gases to etchthe exposed metal layer disposed on the substrate while providing asufficiently low power level, compared to prior art metal etchprocesses, for the substrate temperatures to be about 150° C. or less.

Generally, a bias power of less than about 200 watts, for examplebetween about 0 watts and about 150 watts, is applied to the substrateto increase directionality of the etching radicals with respect to thesurface of the substrate. A bias power of less than 50 watts, such asbetween about 20 watts and about 40 watts, may be used in the etchingprocess. A bias between about 25 watts and 35 watts has been observed toprovide sufficient directionality of etching radicals during the etchingprocess.

The exposed material of the substrate surface may be etched by theplasma of the processing gases for between about 15 seconds and about400 seconds, for example, between about 30 seconds and about 350seconds, depending on the quantity of material to be etched. Any ARClayer material may be exposed to the plasma of the first processing gasfor between about 5 seconds and about 180 seconds, for example betweenabout 30 seconds and about 60 seconds, which may in addition to orinclusive of the total etching time.

Generally, the processing chamber pressure is maintained between about 2milliTorr and about 50 milliTorr, preferably between about 2 milliTorrand about 20 milliTorr, for example, between about 3 milliTorr and about8 milliTorr may be maintained during the etching process.

The substrate is also maintained at a temperature of about 150° C. orless during processing. A substrate temperature below about 150° C. orless has minimal heat degradation of materials, such as resistmaterials, deposited on the substrate during the photolithographicreticle fabrication processes with the processing gases describedherein. The substrate temperature between about 20° C. and about 150°C., preferably between about 20° C. and about 50° C., may be used toetch photomask features with minimal heat degradation of materialdisposed on the substrate surface. Additionally, the sidewalls of theprocessing chamber are preferably maintained at a temperature of lessthan about 70° C., and the dome is preferably maintained at atemperature of less than about 80° C. to maintain consistent processingconditions and to minimize polymer formation on the surfaces of theprocessing chamber.

An example of the etching process is described as follows. The substrateis disposed on the support member 16 and a processing gas as describedherein is introduced into the chamber and a plasma is generated ormaintained to etch the metal layer 320 by introducing a processing gasof oxygen gas (O₂), chlorine gas (Cl₂), hydrogen bromide (HBr), andoptionally, an inert gas, such as argon (Ar) or helium (He) at a flowrate between about 100 sccm and about 200 sccm and generating a plasma.Oxygen gas may be introduced into the processing chamber at a flow ratebetween about 5 sccm and about 50 sccm, chlorine gas may be introducedinto the processing chamber at a flow rate between about 5 sccm andabout 100 sccm, and hydrogen bromide gas may be introduced into theprocessing chamber at a flow rate between about 5 sccm and about 100sccm. The inert gas, for example, helium, is introduced into theprocessing chamber at a flow rate between about 25 sccm and about 70sccm. The ratio of chlorine gas to hydrogen bromide in the processinggas is between about 10:1 and about 0.5:1.

The plasma is generated by applying a source RF power between about 250watts and about 650 watts, for example 400 watts, to an inductor coil togenerate and sustain a plasma of the processing gases during the etchingprocess. A bias power between about 20 watts and about 40 watts, forexample about 20 watts, is applied to the substrate support. The etchingprocess is performed between about 90 seconds and about 400 seconds, forexample, about 350 seconds. Endpoint of the metal layer 320 etchingprocess may be monitored by an optical emission endpoint control.

Generally, the processing chamber pressure is maintained between about 2milliTorr and about 20 milliTorr, for example, at about 3 milliTorr,about 5 milliTorr, or about 8 milliTorr. The substrate temperature isbetween about 20° C. and about 100° C. during the etching process.Additionally, the sidewalls 15 of the processing chamber 10 aremaintained at a temperature of less than about 70° C. and the dome ismaintained at a temperature of less than about 80° C. The abovedescribed metal etching process generally produces a selectivity ofmetal layer to resist of about 3:1 or greater.

Alternatively, an overetch step may be performed after the etchingprocess to ensure removal of all of the desired material from thesubstrate. The overetch may use any suitable processing gas for etchingthe metal layer 320. For example, the overetching gas may comprise oneor more, including all, of the oxygen containing gas, the chlorinecontaining gas, the chlorine free halogen containing gas, and the inertgases described herein.

Alternatively, if an ARC material as described herein is formed on themetal layer, the ARC material may be removed with the metal layer duringthe metal layer etching process or may be removed by an etching processbefore etching of the metal layer. An example of a ARC etching processand metal layer etching process is more fully described in U.S. patentapplication Ser. No. 10/803,867, filed on Mar. 18, 2004, and entitled“Multi-Step Process For Etching Photomasks”, which is incorporated byreference to the extent not inconsistent with the claimed aspects anddisclosure herein

The etching process described herein under the conditions disclosedproduces a removal rate ratio, i.e., selectivity or etch bias, of metallayer to resist of about 1:1 or greater. A selectivity of metal toresist of about 1:1 or greater has been observed in substrate processedby the etching process described herein. A selectivity of metal toresist of about 3:1 or greater has been observed in substrate processedby the etching process described herein. The increased selectivityresults in the etching processes preserve the critical dimensionpatterned in the photoresist layer and allows for etched chromiumfeatures to have the desired critical dimensions.

The etching processes as described herein were also observed to remove“top” or upper surface resist material independent of “side” withinfeature resist material, which is consistent with anisotropic etchingand improved feature formation. Additionally, processed substrates haveproduced features with the desired critical dimensions with an almostvertical profile, i.e., an angle of about 90° between the sidewall ofthe feature and the bottom of the feature compared to prior art resultof about 85° to about 88°.

Optionally, a plasma strike may be used to generate the plasma foretching the metal layer 320. A plasma strike may be used to initiate orgenerate the plasma prior to introducing the processing gas at thecompositions and flow rates described herein for the etching process.The plasma strike may use an inert gas or a composition of theprocessing gases described herein.

The processing conditions and the plasma conditions of the plasma strikeprocess may approximate those of the etching process with the processinggas described herein including processing gas constituents of theprocessing gas, total flow rates, chamber pressures, source power, andbias power. The plasma strike process may be for about 15 seconds orless, such as between about 3 seconds and about 5 seconds. An example ofplasma striking includes establishing the chamber pressure between about2 milliTorr and about 50 milliTorr, for example, between about 20milliTorr and about 30 milliTorr, supplying a source power to a coil ata range between about 250 watts and about 1000 watts, such as about 400watts, and/or supplying a bias at a range between about 1 watt and about50 watts, such as between about 20 watts and about 40 watts. The sourcepower used to strike the plasma may be less than the power used duringetching of the substrate.

After etching of the metal layer 320 is completed, the substrate 300 istransferred to a processing chamber, and the remaining resist material330 is usually removed from the substrate 300, such as by an oxygenplasma process, or other resist removal technique known in the art asshown in FIG. 3D.

Optionally, an attenuating material may used to form an attenuatingphase shift photomasks to increase the precision of the etching patternformed on the substrate by increasing the resolution of the lightpassing through the photomask. An attenuating material, such asmolybdenum silicide (MoSi) or derivative may be disposed between theopaque metal layer 320 and the optically transparent substrate surface310 may then be etched. The attenuating material may be deposited on theoptically transparent substrate or may be integrated in the opticallytransparent substrate during manufacturing of the optically transparentsubstrate. For example, if an attenuating material is disposed on thesubstrate surface prior to deposition of the metal layer 320, theattenuating material may be formed by depositing and patterning a secondphoto resist material on the now patterned metal layer 320 to expose theunderlying material at step 250. The underlying material of theattenuating material, or the exposed substrate itself if appropriate,may be then be etched with an etching gases suitable for such materialsat step 260.

An example of etching the optically transparent material, such assilicon-based material, and attenuating materials of the substrate ismore fully described in U.S. patent application Ser. No. 10/437,729,filed on May 13, 2003, and entitled “Methods For EtchingPhotolithographic Reticles”, and U.S. Pat. No. 6,391,790, filed on May21, 2002, which are incorporated by reference to the extent notinconsistent with the claimed aspects and disclosure herein.

The above described processing gas composition and processing regime isbelieved to provide controllable etching of openings or patterns withdesired critical dimensions. The etching of the openings or patterns isgenerally anisotropic with the use of the processing gas describedherein. The anisotropic process removes material deposited on the bottomof the opening at a higher rate than material on the sidewalls of theopening. This results in materials on the sidewalls of the openingsbeing removed at a lower rate than materials on the bottoms of openings.An etch process that etches the sidewalls of the openings at a slowerrate will be less likely to overetch the sidewalls allowing for improvedpreservation of the critical dimensions of the openings being etched,and, thus, reducing etching bias.

The invention is further described by the following examples that arenot intended to limit the scope of the claimed invention.

EXAMPLES

A photolithographic reticle including a substrate made of an opticallytransparent material, such as optical quality quartz, fused silica,molybdenum silicide, molybdenum silicon oxynitride (MoSi_(X)N_(Y)O_(Z)),calcium fluoride, alumina, sapphire, or combinations thereof, with achromium photomask layer, for example, between about 70 nanometers (nm)and about 100 nm thick disposed thereon, is introduced into a processingchamber for resist deposition. An optional ARC layer of chromiumoxynitride, which may comprise up to about 25% of the total chromiumdepth, may be formed.

A resist, such as ZEP, a resist material commercially available fromTokyo-Oka of Japan, or a chemically amplified resist or CAR resist alsocommercially available from Tokyo-Oka of Japan, is deposited upon thechromium oxynitride layer and then patterned using conventional laser orelectron beam patterning equipment. The resist deposited on thesubstrate is between about 200 nm and about 600 nm thick, for example,between about 300 nm and about 400 nm thick, but may be of any thicknessdesired.

Example 1

The reticle is placed in an etch chamber such as the DPS™ metal etchchamber described above. The patterned substrate also described above isplaced on the cathode pedestal of the etch chamber, and the chamber ismaintained at a pressure between about 8 milliTorr. A plasma wasgenerated by applying a source RF voltage to the inductor coil at apower level of about 400 watts. A bias power of 20 watts was applied tothe cathode pedestal. The substrate surface is maintained at atemperature between about 20° C. and about 50° C. The chamber walls anddome were cooled to less than about 70° C. to maintain a steady etchprocessing condition. The etching of the opening occurred under thefollowing gas flows:

Oxygen (O₂), at 12 sccm

Chlorine gas (Cl₂), at 96 sccm

Hydrogen bromide (HBr), at 10-50 sccm.

The total flow rate was between about 158 sccm for the above listedprocessing gases. The etching process was performed for about 350seconds form the openings in the metal layer.

Example 2

The reticle is placed in an etch chamber such as the DPS™ metal etchchamber described above. The patterned substrate also described above isplaced on the cathode pedestal of the etch chamber, and the chamber ismaintained at a pressure between about 5 milliTorr. A plasma wasgenerated by applying a source RF voltage to the inductor coil at apower level of about 400 watts. A bias power of 20 watts was applied tothe cathode pedestal. The substrate surface is maintained at atemperature between about 20° C. and about 50° C. The chamber walls anddome were cooled to less than about 70° C. to maintain a steady etchprocessing condition. The etching of the opening occurred under thefollowing gas flows:

Oxygen (O₂), at 12 sccm

Chlorine gas (Cl₂), at 96 sccm

Hydrogen bromide (HBr), at 40 sccm.

The total flow rate was between about 148 sccm for the above listedprocessing gases. The etching process was performed for about 350seconds form the openings in the metal layer.

Example 3

The reticle is placed in an etch chamber such as the DPS™ metal etchchamber described above. The patterned substrate also described above isplaced on the cathode pedestal of the etch chamber, and the chamber ismaintained at a pressure between about 5 milliTorr. A plasma wasgenerated by applying a source RF voltage to the inductor coil at apower level of about 600 watts. A bias power of 20 watts was applied tothe cathode pedestal. The substrate surface is maintained at atemperature between about 20° C. and about 50° C. The chamber walls anddome were cooled to less than about 70° C. to maintain a steady etchprocessing condition. The etching of the opening occurred under thefollowing gas flows:

Oxygen (O₂), at 12 sccm

Chlorine gas (Cl₂), at 96 sccm

Hydrogen bromide (HBr), at 50 sccm.

The total flow rate was between about 158 sccm for the above listedprocessing gases. The etching process was performed for about 350seconds form the openings in the metal layer.

While the foregoing is directed to the exemplary aspects of theinvention, other and further aspects of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method etching a chromium-containing layer, comprising: positioninga substrate having a chromium-containing layer disposed thereon in aprocessing chamber, and a patterned resist material disposed on thechromium-containing layer and exposing a portion of thechromium-containing layer; forming a plasma from an oxygen containinggas, a chlorine containing gas, and a chlorine-free halogen containinggas selected from the group consisting of hydrogen bromide, hydrogeniodide, and combinations thereof, with a molar ratio of chlorine gas tochlorine-free halogen containing gas between about 10:1 and about 0.5:1by applying power to a coil and a bias to a substrate support in theprocessing chamber; and etching the chromium-containing layer in thepresence of the plasma.
 2. The method of claim 1, wherein thechromium-containing layer is a chromium material selected from the groupconsisting of chromium, chromium oxynitride, and combinations thereof.3. The method of claim 1, wherein forming the plasma further comprises:forming the plasma from at least one of oxygen, carbon monoxide, andcarbon dioxide; forming the plasma from at least one of chlorine, carbontetrachloride and hydrogen chloride; and forming the plasma from atleast one of hydrogen bromide and hydrogen iodide.
 4. The method ofclaim 1, wherein forming the plasma further comprises: forming theplasma from oxygen, chlorine, and hydrogen bromide.
 5. The method ofclaim 1, wherein forming the plasma further comprises: forming theplasma from at least one of helium, argon, xenon, neon and krypton. 6.The method of claim 1, wherein forming the plasma further comprises:applying a source RF power between about 100 watts and about 1000 wattsto a coil in the processing chamber; and applying a bias power betweenabout 0 watts and about 150 watts to a substrate support disposed in theprocessing chamber.
 7. The method of claim 1, wherein etching thechromium-containing layer further comprises: removing thechromium-containing layer relative to patterned resist layer at a ratioof between about 1:1 and about 3:1.
 8. The method of claim 1 furthercomprising: a patterned antireflective coating disposed between thechromium-containing layer and the patterned resist layer; etching thechromium-containing layer through an anti-reflective coating; andetching the anti-reflective coating during the etching of thechromium-containing layer.
 9. The method of claim 8, wherein theanti-reflective coating is chromium oxynitride.
 10. The method of claim1, wherein the substrate is optically transparent.
 11. The method ofclaim 10, wherein the optically transparent substrate comprises asilicon-based material selected from the group consisting of quartz,molybdenum silicide, molybdenum silicon oxynitride, and combinationsthereof.
 12. A method for etching a chromium-based layer, comprising:positioning an optically transparent silicon-based substrate having achromium-based layer on a support member in a processing chamber,wherein the chromium-based layer has a patterned resist materialdeposited thereon and exposing a portion of the chromium-based layer;forming a plasma from a processing gas comprising chlorine gas, oxygengas, and hydrogen bromide with a molar ratio of chlorine gas to hydrogenbromide gas between about 10:1 and about 0.5:1 ; and etching exposedportions of the chromium-based layer at a removal rate ratio ofchromium-based layer to resist material of about 1:1 or greater.
 13. Themethod of claim 12, wherein the processing gas further comprising atleast one of an inert gas selected from the group consisting of helium,argon, xenon, neon, krypton, and combinations thereof.
 14. The method ofclaim 12 further comprising: a layer of MoSi disposed between theoptically transparent silicon-based substrate and the chromium-basedlayer.
 15. The method of claim 12, wherein the chromium-based layercomprises chromium, chromium oxynitride, or combinations thereof, andthe optically transparent silicon-based substrate comprises quartz,molybdenum silicide, molybdenum silicon oxynitride, or combinationsthereof.
 16. The method of claim 15, wherein the substrate furthercomprises an anti-reflective coating of chromium oxynitride.
 17. Amethod for processing a chromium layer, comprising: positioning areticle on a support member in a processing chamber, wherein the reticlecomprises a chromium-based photomask layer formed on an opticallytransparent silicon-based material, the chromium-based photomask layerhaving a patterned resist material deposited thereon and exposing aportion of the chromium-based photomask layer; introducing a processinggas comprising chlorine gas, oxygen gas, and hydrogen bromide;maintaining a chamber pressure between about 3 milliTorr and about 8milliTorr; delivering a source power of about 400 watts to a coildisposed in the processing chamber to generate a plasma; supplying abias power to the support member of about 20 watts; and etching exposedportions of the chromium-based photomask layer.